To be honest, I don't know the precise answer to the questions that you posed above, but suffice to say that we must require at least 10 each of Captains and FO's just to crew the two new a/c (one of which, G-IGOS, was delivered yesterday).
Then to cover any flight crew that are leaving (for what ever reasons) we will need a few more (maybe 3 or 4'ish of each rank), plus recruitment of permanent crew (to replace the contract pilots that we employ - say another 5 again, of each rank).
So, perhaps a guess at maybe 20 of each rank might not be too far out - but don't quote me, because (not being management) I don't actually know the precise figures.
Ps. Our recruitment is actively underway and has been for many months (we don't normally advertise, they apply to us - in considerably numnbers too); thus, for all that I know, they might already have filled many of the above vacancies.